Plasterboard faced with lightweight paper



Oct. 5, 1943. D. D. CRANDELL -PLASTER BOARD FACED WITH LIGHTWEIGHT PAPERFiled Dec. 19, 1941 Dcm-S). @EEiEm,

ATTORNEYS Patented Oct. 5, 1943 V UNITED STAT ,PLASTERBOARD'FACED WITHLIGHT- WEIGHT PAPER Dean 1). Crandell, Buflalo, N. Y., assignor toNational Gypsum Company, Buflalo, N. Y.

Application December 19,- 1941, Serial No. 423,642

5 Claims. (Cl. 154-454 The present invention relates to an improvedplaster board and more particularly a plaster board in which the core ofset cementitious material' is faced with lightweight paper having.relatively high crosswise strength and relatively high porosity.

In the manufacture of wall board from cementitious materials, such ascalcined gypsum, it has been the practice heretofore to prepare a mix ofcalcined gypsum and water and to run this mix between upper and lowerfacing sheets producing,

upon setting or crystallization of the calcined gypsum, .a wall board orplaster board having a set core with facing sheets enclosing the coreand bonded thereto in order to decrease the frangibility of thecementitious core.

Due to the fact that these facing paper sheets possess a greaterlengthwise than crosswise strength and are fed lengthwise of the boardmaking machine: the crosswise strength of the board with the paperfacing sheet attached is less than the lengthwise strength. It has beengeneral practice, therefore, to provide a facing paper having acrosswise strength of at least 25 pounds per square inch as'determinedon Standard Scott tensile strength machine in order 'to produce setplaster board that is sufliciently resistant to fracture to be employedfor usual purposes of such wall board.

It has been the general practice to employ, as facing sheets for gypsumlath, the weakest type of gypsum wall board, paper made of so-calledchip stock made on a cylinder machine and having a weight of about62pounds per thousand square feet of paper and athickne'ss of about 0.020inch in order to obtain paper possessing the requisite 25 poundscrosswise strength. Such paper, since it is made on a cylinder machine,possesses a lengthwise strength, that is, strength measured in themachine direction, of about 80 pounds, a figure much higher than isnecessary to produce satisfactory board. Such a paper produces a gypsumlath which when tested by procedure well known in the industry andoutlined in Federal Specification SSW 51 A will have atransversejstrength lengthwise with the fibers of approximately 100pounds and crosswise of 40 pounds. Thinner and lighter paper made ofbait stock has not been foundsatisfactory as facing sheets-due to thetendency of the paper to pull away from the board and form corrugationsand due to difficulty encountered in drying the flnishedboard.

It is obvious that the wide difference between the two directional streh accomplishes no}- satisfactory results. Therefore it'is advanta geousto produce and employ a facing-sheet on which the crosswise strength ismaintained up to, or is superior to, the present acceptable minimum.This is accomplished, in accordance with the present invention, by theuse of a Fourdrinier sheet made at 55 pounds lengthwise and 35 poundscrosswise strength which produces a lath possessing a crosswise strengthof 50-55 pounds and a lengthwise strength of -80 pounds.

Recently suggestions have been made to use combinations of plies of chipand kraft paper in order to obtain a facing sheet with the requisitecrosswise strength and having a unit weight considerably below the 62pounds normally employed. However, since such paper is made in plies itis subject to the disadvantage of all cylinder paper, namely, to splitand separate into the constituent lamellae. j.

It is an object of the present invent-ion to provide a wallboard facedwith paper of a Weight considerably below that heretofore thoughtnecessary to provide the requisite crosswise strength and which is notsubject to splitting into plies.

It is a further object of the invention to provide a wall board facedwith paper made of combined chip and kraft stock and having suflicientporosity to permit of eflicient and rapid drying.

In the drawing:

Fig. 1 is an enlarged sectional view of wall board of the presentinvention, and

Fig. 2 shows the forming end of a wall board machine and illustratesdiagrammatically the feed of the plastic core between facing sheets.

In accordance with the present invention a cementitious mix is preparedin. a conventional way from calcined gypsum and water to which may beadded, if desired, paper pulp, starch and foaming ingredients, all. asis well known in the art. The cementitious mix is thereafter fed betweenthe improved facing sheet, more fully described hereinafter, possessinga crosswise strength of about 30 to 35 pounds and a lengthwise strengthof about 52 to 57 pounds or higher,

the paper having a weight of about 38 to 45.

length desired and fed to a conventional drying oven where the excessfree water not combined as water crystallization is removed.

The product thus formed is a wall board or plaster board having acrosswise strength equivalent to that made from calcined gypsum andwater and faced with 62 pound chip paper of a caliper of 0.019 to 0.020,board that has been found eminently satisfactory in industrial uses.

The paper employed as facing sheets II and M for the plaster core 20 isadvantageously prepared from about 30 to 50% by weight of chip fiberswhich may be obtained from waste-newspaper stock, and the like, andabout 50 to 70% by weight of kraft fibers. This stock is prepared in theusual way in suitable breaker heaters, deckers, and finish heaters towhich latter the appropriate amount of size, alum and coloring,

if desired, may be added and the fiber-water ratio adjusted prior tofeeding the stock to the head box of aconventional Fourdrinier machine.Suiiicient stock is run under the slice bar to the wire of theFourdrinier machine to produce a finished paper of about 40 pounds perthousand square feet in weight and having a caliper of about 0.016".Upon test this paper is found to possess a minimum crosswise strength ofabout 32 pounds and a lengthwise strength (machine direction) of about55 pounds. Since the paper is made on a Fourdrinier machine it is notformed as individual plies but represents one single ply not subject tosplitting.

Paper made of this composition on a'Fourdrinier machine is especiallysuitable for facing sheets for wall board since the paper is relativelyporous and due tothe low caliper permits of more rapid drying of thecompleted Wall board in the kiln. The increased rate of drying willbecome apparent when it is understood that the improved facing papershows a 20 second densometer test, that is 100 c. c. of air under aconstant specified pressure will flow through the paper sheet in 20seconds as contrasted with a 90 second densometer test'for normal chipsheets made on a cylinder machine.

- From the above it will be seen that the present invention provides. aplaster board that is faced It will further be seen that the porosity ofthe paper permits'of more rapid drying of the board and therefore of anincrease of the machine speed with consequent greater production from agiven machine.

What is claimed is:

1. Wall board comprising a set cementitious core and a paper sheetbonded to one face of the core, said sheet comprising paper of theFourdrinier type of a pulp composition comprising about 30-50% chipstock and about 50-70% kra t stock by weight and having a weight 01' 35to 4 pounds per thousand square feet, a crosswis strength of about 28-35poundsand a densom eter test of in the neighborhood of 20 seconds.

2. Wall board comprising a set cementitious core and a paper sheetbonded to one face of the core, said'sheet comprising paper of theFourdrinier type and having a weight of 35 to 45 pounds per thousandsquare feet, a crosswise strength of about 28 to 35 pounds and acomposition of mixed kraft and chip stock producing a densometer test ofin the neighborhood of 20 seconds.

3. Wall board comprising a set cementitious core and a paper sheetbonded to one face of the core, said sheet comprising paper of theFourdrinier type of a pulp composition comprising about 30-50% chipstock and about -70% kraft stock by weight and having a crosswisestrength of above 28 pounds and a weight of 35 to 45 pounds per thousandsquare feet.

4. Wall board comprising a set cementitious core ands. paper sheetbonded to one face of the core, said sheet comprising paper of a pulpcomposition comprising about 3050% chip stock and about 50-70% kraftstock by weight and having a crosswise strength of about 28-35 poundsand a thickness of about 0.015 to 0.016 inch.

5. Wall board comprising a set cementitious core and a paper sheetbonded to one face of the densometer test in the neighborhood of 20secwith a type of paper which will not separate into Y plies when theboard is scored preparatory to breaking as is usual on thejob, one whichdoes not scuif easily and one which ,will not pull away into lamellaeupon withdrawal of the cutting knife of the board machine.

onds, said paper sheet having a weight of 35 to 45 pounds per thousandsquare feet, a crosswise strength of 28-35 pounds and a thickness ofabout 0.015 to 0.016 inch.

DEAN D. .CRAN'DELL.

